Electricity Paper2 (set 1) 1. This question is about electric circuits. (a) Define (i) electromotive force (emf ) of a battery. (1) (ii) electrical resistance of a conductor. (1) (b) A battery of emf ε and negligible internal resistance is connected in series to two resistors. The current in the circuit is I. (i) State an equation giving the total power delivered by the battery. (1) IB Questionbank Physics 1
(ii) The potential difference across resistor R 1 is V 1 and that across resistor R 2 is V 2. Using the law of the conservation of energy, deduce the equation below. ε = V 1 + V 2 IB Questionbank Physics 2
(c) The graph shows the I-V characteristics of two conductors, X and Y. On the axes below, sketch graphs to show the variation with potential difference V of the resistance of conductor X (label this graph X) and conductor Y (label this graph Y). You do not need to put any numbers on the vertical axis. (3) IB Questionbank Physics 3
(d) The conductors in (c) are connected in series to a battery of emf ε and negligible internal resistance. The power dissipated in each of the two resistors is the same. Using the graph given in (c), (i) determine the emf of the battery. (ii) calculate the total power dissipated in the circuit. (Total 12 marks) IB Questionbank Physics 4
2. This question is about electrical resistance. (a) A resistor of resistance 1.5 Ω is made from copper wire of radius 0.18 mm. The resistivity of copper is 1.7 10 8 Ω m. Determine the length of copper wire used to make the resistor............. (b) The manufacturer of the resistor in (a) guarantees that the resistance is within 10 % of 1.5 Ω, provided that the power dissipation in the resistor does not exceed 1.0 W. (i) Suggest why the resistance of the resistor might be greater than 1.65 Ω if the power dissipation in the resistor is greater than 1.0 W. (ii) Show that, for a power dissipation of 1.0 W, the current in a resistor of resistance 1.5 Ω is 0.82 A. (1) IB Questionbank Physics 5
(iii) The 1.5 Ω resistor is connected in series with a variable resistor and battery of emf 6.0 V and internal resistance 1.8 Ω. Estimate the resistance R of the variable resistor that will limit the current to 0.82 A. (3) (Total 8 marks) 3. This question is about electric circuits The components shown below are to be connected in a circuit to investigate how the current I in a tungsten filament lamp varies with the potential difference V across it. IB Questionbank Physics 6
(a) Construct a circuit diagram to show how these components should be connected together in order to obtain as large a range as possible for values of potential difference across the lamp. (4) (b) On the axes, sketch a graph of I against V for a filament lamp in the range V = 0 to its normal working voltage. (c) The lamp is marked with the symbols 1.25 V, 300 mw. Calculate the current in the filament when it is working normally.......... (1) IB Questionbank Physics 7
(d) The resistivity of tungsten at the lamp s working temperature is 4 10 7 Ωm. The total length of the tungsten filament is 0.80 m. Estimate the radius of the filament................ (4) (e) The cell is connected to two identical lamps connected in parallel. The lamps are rated at 1.25 V, 300 mw. The cell has an emf of 1.5 V and an internal resistance of 1.2 Ω. Determine whether the lamps will light normally................ (4) (Total 15 marks) IB Questionbank Physics 8
4. Domestic shower (a) The diagram below shows part of the heating circuit of a domestic shower. Cold water enters the shower unit and flows over an insulated heating element. The heating element is rated at 7.2 kw, 240 V. The water enters at a temperature of 14 C and leaves at a temperature of 40 C. The specific heat capacity of water is 4.2 10 3 J kg 1 K 1. (i) Define specific heat capacity. (1) (ii) Estimate the flow rate of the water. (4) IB Questionbank Physics 9
(iii) Suggest two reasons why your answer to (a)(ii) is only an estimate. 1....... 2....... (iv) Calculate the current in the heating element when the element is operating at 7.2 kw. (v) Explain why, when the shower unit is switched on, the initial current in the heating element is greater than the current calculated in (a)(iv). IB Questionbank Physics 10
(b) In some countries, shower units are operated from a 110 V supply. A heating element operating with a 240 V supply has resistance R 240 and an element operating from a 110 V supply has resistance R 110. Show that for heating elements to have identical power outputs R R 110 = 240 0.21......................... (3) (Total 14 marks) IB Questionbank Physics 11
5. (a) Draw the complete diagram of the circuit that uses a potential divider, ammeter, voltmeter and cell to measure the current-voltage characteristics for component X. (3) IB Questionbank Physics 12
(b) The graph shows the current-voltage characteristics for the component X. Component X is now connected across the terminals of a cell of emf 2.0 V and negligible internal resistance. Use the graph to show that the resistance of X is 0.83 Ω............. (c) A resistor of constant resistance 1.0 Ω is connected in series with the cell in (b) and with X. Use the graph to deduce that the current in the circuit is 1.3 A................ (3) (Total 8 marks) IB Questionbank Physics 13